Process for producing electrorefined nickel having controlled size

ABSTRACT

AN IMPROVED PROCESS FOR PRODUCING ELECTROREFINED NICKEL CATHODE MATERIAL OF CONTROLLED DIMENSION AND SUBSTANTIAL THICKNESS WHEREIN THE NICKEL IS DEPOSITED UPON A SUBSTANTIALLY FLAT, PERMANENT METAL CATHODE MANDREL SUCH AS STAINLESS STEEL, AND HAVING CONDUCTIVE ISLANDS OF CONTROLLED SIZE DEFINED ON THE SURFACE THEREOF, E.G., BY THE USE OF INTERCONNECTING LINES OF NONCONDUCTIVE RESIST, FROM A NICKEL ELECTROEFINING CATHOLYTE CONTAINING CONTROLLED AMOUNTS OF SULFUR DIOXIDE AND A LEVELING AGENT TO FACILITATE ADHERENCE OF THE ELECTRODEPOSITED NICKEL UPON THE MANDREL SURFACE BY CONTROLLING THE STRESS LEVEL THEREIN TO A TENSILE VALUE NOT EXCEEDING ABOUT 6,000 POUNDS PER SQUARE INCH AND THEREAFTER STRIPPING THE NICKEL DEPOSIT FROM THE MANDREL TO RECOVER ELECTRODEPOSITED NICKEL IN SIZES CORRESPONDING TO THE ORIGINAL AREAS OF THE CONDUCTIVE ISLANDS AND TO RECOVER THE MANDREL IN A CONDITION SUITABLE FOR FURTHER PLATING.

United States Patent 3,577,330 PROCESS FOR PRODUCING ELECTROREFINEDNICKEL HAVING CONTROLLED SIZE Burton Bower Knapp, Allendale, N..l., andLeander Ernest Cupp, Port Colborne, Ontario, Canada, assignors to TheInternational Nickel Company, Inc., New York, N.Y. No Drawing.Continuation-impart of application Ser. No. 338,309, Jan. 17, 1964. Thisapplication Nov. 17, 1967, Ser. No. 683,801

Int. Cl. C2211 1/14; C23b 7/08 U.S. Cl. 204-112 7 Claims ABSTRACT OF THEDISCLOSURE An improved process for producing electrorefined nickelcathode material of controlled dimension and substantial thicknesswherein the nickel is deposited upon a substantially flat, permanentmetal cathode mandrel such as stainless steel, and having conductiveislands of controlled size defined on the surface thereof, e.g., by theuse of interconnecting lines of nonconductive resist, from a nickelelectrorefining catholyte containing controlled amounts of sulfurdioxide and a levelling agent to facilitate adherence of theelectrodeposited nickel upon the mandrel surface by controlling thestress level therein to a tensile value not exceeding about 6,000 poundsper square inch and thereafter stripping the nickel deposit from themandrel to recover electrodeposited nickel in sizes corresponding to theoriginal areas of the conductive islands and to recover the mandrel in acondition suitable for further plating.

The present application is a continuation-in-part application of acopending U.S. application Ser. No. 338,- 309, filed J an. 17, 1964, nowabandoned.

The present invention relates to the production of electrolytic nickeland, more particularly, to a process for producing electrolytic nickelin subdivided form.

It is well known that the standard commercial high purity nickel (99.4+%nickel) is usually provided in the form of cathode sheets from anelectrorefining operation. These sheets are usually about 28 inches by38 inches in major dimension and are about inch thick. In manyindustrial operations, these cathode sheets can be employed directly.However, in many other industrial operations, nickel must be provided insmaller sizes because the standard size cannot conveniently be used. Thestandard cathode sheets can be sheared to provide the smaller sizesrequired in operations such as induction furnace melting ofnickel-containing alloys, nickel stock for electroplating using titaniumbaskets to hold the nickel stock, etc. However, it is desirable toprovide electrolytic nickel in smaller sizes directly from theelectrorefining operation while at the same time maintaining orimproving the efficiency of the nickel electrorefining operation, and,thus, to eliminate the cost factors involved in shearing the standardcathode nickel sheets. The production of electrolytic nickel is wellknown and is described, for example, in the Renzoni U.S. Pat. No.2,394,874.

It has now been discovered that through the use of a permanent cathodemandrel of special design, electrolytic nickel pieces of any desiredsize can be produced directly in the electrorefining operation whilemaintaining the efficiency of the operation at a high level.

It is an object of the present invention to provide a process forproducing electrolytic nickel of controlled small size.

Another object of the invention is to provide a special permanentmandrel for use as cathode in a nickel electrorefining cell.

The invention also contemplates providing a process for producingelectrolytic nickel having :a low level of internal stress.

Other objects and advantages of the invention will become apparent fromthe following description.

Generally speaking, the present invention contemplates a process forproducing electrolytic nickel in subdivided form which comprisesimmersing in an electrorefining bath a permanent, i.e., reusable, metalcathode mandrel having conductive islands defined on the surfacethereof, electrodepositing nickel upon said cathode under conditions oflow stress to provide electrolytic nickel deposits having substantialthickness upon said conductive islands, removing the plated cathodemandrel from said bath and removing the deposited nickel from saidmandrel, so as to recover the mandrel for reuse.

The conductive islands are defined on the surface of the permanent metalcathode mandrel by means of interconnecting areas of nonconductivematerial. The mandrel may be provided in a number of ways. Thus,interconnecting lines of nonconductive or resist material at least aswide as the thickness of metal to be deposited upon the mandrel (i.e.,generally about /s to 4 inch) may be applied to the surface thereof todefine isolated conductive areas, or islands, of the desired size andshape. The nonconductive resist material may be in the form of anadherent paint, varnish, lacquer, tape, etc., which will be retained onthe mandrel surface and will be compatible with the electrorefiningbath. Materials having a plastic or rubber base, e.g., epoxy resin,sacrylics, polyethylenes, etc., are examples of such resists. Theconductive cathode metal mandrel may be, for example, pure nickel or anickel-chromium or nickel-chromium-iron alloy containing about 8% to 30%chromium, at least 8% nickel and up to about 74% iron, such as thewell-known 18-8 stainless steel. Electroformed nickel is alsosatisfactory as the mandrel metal. In order that the mandrel will besufiiciently rugged to withstand repeated reuse, it is usually about0.020 inch or about 0.040 inch up to about or about /8 inch thick. Themandrel may be sufliciently thin, e.g., up to about inch thick, to bereadily flexed for stripping the nickel deposit therefrom or may beconsiderably thicker and stiffer, e.g., about inch thick. A pattern ofinterconnecting lines which are depressed with respect to a major faceof the mandrel may be embossed in the thinner mandrel sheets and theembossed lines may be filled or coated with resist. In such an instance,the mandrel may be made of two embossed sheets placed back-to-back sothat plating may be conducted simultaneously upon both sides of themandrel. Such embossed lines also perform the function of stifiening thethinner mandrel. It is advantageous to electroform mandrels containingsuch depressed interconnecting lines in a metal such as nickel. It is anadvantage from the operating standpoint to employ the thicker andheavier mandrel sheets in electrorefining practice since good contact tothe cathode bus bar is thereby achieved and the problem of warping andshorting in the plating tank is avoided. In order to promote adherenceof the electrodeposited nickel to the mandrel, the mandrel surfaceadvantageously has a surface finish in the range of about 10 to aboutmicroinches. Such a surface finish can be provided by the mill or can beobtained by means such as scratch brushing, light sand blasting, etc.

In carrying the invention into practice, it is preferred to depositelectronickel in a low-stress condition so that satisfactory adherenceof the electrolytic nickel upon the exposed cathode areas will beachieved. Thus, it is advantageous that the tensile stress level in thedeposit be not higher than about 6,000 pounds per square inch (p.s.i.)and between about 8,000 psi. compressive and about 6,000 p.s.i. tensileas measured by the Brenner-Senderoff contractometer. When stress iscontrolled to this low level, cathode nickel segments as large as about2 inches by 2 inches can be produced without encountering separation ofthe cathodenickel segments from the cathode sheet during the platingoperation. It will be appreciated that the size of the conductivecathode areas, or islands, which may successfully be employed withoutencountering undesirable separation of the electrolytic nickel segmentsdeposited thereon, varies in relation to the stress level which ismaintained in the deposit. Thus, when lower tensile stress levels than6,000 p.s.i. are maintained in the deposit, cathode nickel segments inchto inch in thickness and larger than 2 inches by 2 inches can beproduced successfully, i.e., without encountering separation of thedeposit from the mandrel during the plating operation. A tendency forlifting of nickel electrodeposits having a rectangular shape at cornersof conductive islands has been observed. Accordingly, it is advantageousto employ conductive islands having a circular or elliptical shape.

In order to obtain the required low stress level in the deposit, aconcentration of about 0.005 to about 0.02, e.g., about 0.009 to about0.011, gram per liter (g.p.l.) of sulfur dioxide and about 0.01 to about0.1 g.p.l. of a levelling agent, e.g., hydracarylonitrile, aremaintained in the electrorefining electrolyte. A preferred electrolytealso contains about 40 to about 70 g.p.l. of nickel, about 20 to about55 g.p.l. of chloride ion, about 65 to about 150 g.p.l. of sulfate ion,about to about 25 g.p.l. of boric acid, about 40 to about 60 g.p.l. ofsodium ion, has a pH of about 3 to about 5, with the balance essentiallywater This electrolyte is operated at a temperature of about 100 F. toabout 160 F. at a cathode current density of about 10 to about 35amperes per square foot (a.s.f.).

After the cathode nickel has been grown to the desired thickness on thecathode, the plated cathodes are removed from the electrorefining celland the crop of refined nickel is removed from the cathode sheet. It isfound that, provided proper control of deposit stress level and mandrelsurface finish are exercised, the nickel readily separates from thecathode sheet. Furthermore, the individual nickel segments are readilyseparable along the original resist lines present in the cathode sheetif, in fact, they are adherent one to another. In the case where theresist lines are about the same width as the thickness of the refinednickel deposit, it is found that a load of about 500 pounds appliednormal to the surface of a nickel deposit stripped from the mandrel willsever a A inch thick deposit 12 inches long along a line grown across anoriginal resist line inch wide. When the resist lines applied to themandrel are Wider than the thickness of the final cathode product, thereis little tendency for the individual nickel pieces to adhere to eachother and such pieces may readily be recovered as such during thestripping operation.

The stripping operation itself may be conducted in a number of ways.Thus, flexible plated mandrels may be passed through rubber rolls tostrip the deposit, or they may be flexed in any other convenient mannerto strip the nickel deposit therefrom. Heavier, more rigid mandrels canbe treated by vibration,hammering, etc., to remove the deposittherefrom. As an aid in the stripping operation, the mandrel may betreated before deposition of nickel thereon to reduce adherence ofdeposited nickel thereto. Thus, the mandrel may be dipped in a solutioncontaining about 0.1 to about 1 g.p.l. of sodium dichromate for aboutone minute and then washed with water. This treatment is effective whenused upon mandrels made of nickel, stainless steel and othernickel-chromium and nickelchromium-iron alloys. This treatment alsoassists in promoting the useful life of the mandrel.

For the purpose of giving those skilled in the art a betterunderstanding of the invention and/or a better ap- 4 preciation of theadvantages of the invention, the following illustrative examples aregiven:

EXAMPLE I A nickel electrorefining electrolyte having a pH of about 4-containing about 56 g.p.l. nickel, about 54 g.p.l. chloride ion, aboutg.p.l. sulfate ion, about 50 g.p.l. sodium ion, about 15 g.p.l. boricacid, and the balance essentially water Was prepared. About 0.04 g.p.l.hydracrylonitrile and about 0.01 g.p.l. of sulfur dioxide wereintroduced into the bath. A flat stainless steel cathode mandrel havinga smooth cold rolled surface, about Ms inch thick and having dimensionsof about 29 by 40 /4 inches, was marked off with interconnecting linesof electroplating tape to provide conductive islands about 1 inchsquare. The minimum width of the tape was about A inch. The mandrel wasdegreased, inserted in the bath and plated with nickel using an averagecurrent density of 20 a.s.f. at a temperature of F. to provide a nickeldeposit A3 inch thick on each side of the mandrel. The plated mandrelwas then removed from the bath and the nickel deposit was readilystripped therefrom as individual pieces.

EXAMPLE II in Example I and with a current of about 7,000 amperes beingsupplied to the tank for time suflicient to provide deposits inch thickon each side of each mandrel. At this thickness, the areas ofnonconducting tape were bridged over with nickel. The plated mandrelswere removed from the bath and the deposits stripped therefrom byimpact. The deposits were readily dividable along the locationscorresponding to the original areas of nonconducting tape applied to themandrel and had a roughly hexagonal outline.

The deposit produced according to Examples I and II had a stress levelof about 1,000 p.s.i. tensile and was smooth and white.

The combination of the sulfur dioxide and hydracrylonitrile reagents tocontrol stress level in the deposit is entirely compatible with thestandard sulfate-chloride electrorefining bath and the purificationcycle employed therewith and the bath can be maintained over longperiods of time without diificulty.

The use of the combination of sulfur dioxide and hydracryonitrile asdescribed hereinbefore in the electrorefining bath in accordance withthe invention will introduce controlled amounts of sulfur, e.g., about0.015% to 0.05% sulfur, and more preferably about 0.02% to about 0.025%sulfur, into the deposit and will result in electrolytic nickel havinghigh activity.. This material is in a highly desirable physical form foruse in titanium plating baskets. Furthermore, the material corrodessmoothly in conventional nickel electroplating baths without splittingsince the product contains no physical interruptions such as thestarting sheet contained within usual sheared electrolytic nickel.During plating, the material settles smoothly within the plating basketas the corrosion proceeds so that hangups, bridging and formation ofvoids in the nickel material within the basket are mitigated or areavoided altogether.

It will be appreciated that the method contemplated in accordance withthe present invention provides a number of advantages over theconventional method of shearing a cathode into suitable size. Thus,cathode nickel plated to predetermined size is readily distinguished onthe basis of its physical appearance from sheared nickel. Thus, theindividual nickel pieces have greatly reduced amounts of sharp edges ascompared to the sheared product and have a characteristic peripheralelevated ridge on the outer face of each piece, i.e., the face incontact with the bath, which apparently is created by the lines ofresist present on the mandrel. In addition, the method also provides aready means for applying an identifying mark to each individual piece.This may readily be done by embossing the conductive islands on theflexible mandrel with an identifying mark which is then reproduced inthe deposit. As an economical advantage, the shearing costs such as areattendant to shearing large nickel cathodes to the desired size areeliminated. Furthermore, the step of providing a nickel starting sheetas a separate operation is eliminated since the cathode nickel is grownto its full size in a single operation in accordance with thecontemplation of the present invention.

It will also be appreciated that the electrolytic nickel produced inaccordance with the invention is of substantial thickness, e.g., atleast about inch up to about /2 inch or even thicker, whereas the nickelthickness employed in decorative nickel plating is of a much lowerorder, e.g., only about one to about two thousandths of an inch.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. In the method for electrorefining nickel, the improvement forproducing electrorefined nickel cathode material of controlled dimensionwhich comprises immersing in an electrorefining electrolyte asubstantially flat, permanent metal cathode mandrel having a surfacefinish in the range of about to about 100 microinches and havingconductive islands of controlled size defined on the surface thereof,electrodepositing nickel to a substantial thickness upon the surface ofsaid mandrel while facilitating adherence of said electrodepositednickel upon said mandrel by introducing into said electrolyte controlledproportions of sulfur dioxide and hydrocrylonitrile to control thestress level in said nickel cathode within the range of about 8,000pounds per square inch compressive to about 6,000 pounds per square inchtensile, removing the plated mandrel from the bath and stripping thenickel deposit therefrom to recover electrodeposited nickel in sizescorresponding substantially to the original areas of said conductiveislands and to recover said mandrel in a condition suitable for furtherplating.

2. The method according to claim 1 wherein said electrolyte is asulfate-chloride electrolyte containing about 0.005 to about 0.02 gramper liter of sulfur dioxide and about 0.01 to about 0.1 gram per literof hydracrylonitrile.

3. The method according to claim 2 wherein the sulfur dioxide content ofthe electrolyte is about 0.009 to about 0.011 gram per liter.

4. The method according to claim 1 wherein the mandrel is made of ametal from the group consisting of nickel and alloys containing about 8%to about 30% chromium, at least 8% nickel, and the balance up to about74% iron.

5. The method according to claim 1 wherein the mandrel is made ofstainless steel.

6. The method according to claim 1 wherein the conductive islands in themandrel are defined by interconnecting lines of nonconductive resistmaterial.

7. The method according to claim 6 wherein said conductive islands arecircular or elliptical in shape.

References Cited UNITED STATES PATENTS 2,773,816 12/1956 Wesley et-al.20412 2,706,170 4/ 1955 Marchese 2043 2,392,708 1/ 1946 TSChOp 2042923,419,901 12/1968 Nordblom 20410 3,094,476 6/ 1963 Francis 20412 OTHERREFERENCES Modern Electroplating, 1963, Lowenheim, pp. 270-272.

Technology of Electrodeposition, 1962, Vagramyan et al. p. 267.

Tech. Proceedings A.E.S., 1963, Borchert, p. 44.

HOWARD S. WILLIAMS, Primary Examiner R. L. ANDREWS, Assistant ExaminerU.S. Cl. X.R. 20410 Patent No. 1,577,330 Dated Mi 4 1971 Inventofls) BIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 41, for "99.4+%" read -99.9+%-.

Column 2, line 30, for "resims" read --resins,--.

Signed and sealed this 1 9th day of October 1 971 (SEAL) Attest:

EDWARD M .FLET CHER, JR. ROBERT GOI'TSGHALK Attesting Officer ActingCommissioner of Patents

